During the phase one study, patients will be observed for evidence of efficacy of naloxone and signs of side effects or toxicity of the therapy. All patients will receive an initial dosage of naloxone followed by a 24 hour continuous infusion. The dosage regimen will be increased over nine levels, with larger rates of dosage increase at lower dosage levels. A minimum of three patients will be evaluated at each dose level. If evidence of toxicity develops at a specific dosage level, more patients will be studied at that dose before advancement to a higher dose. If toxicity appears with dose increment, more patients will be studied at a 50% dosage increment over the previous non-toxic dose. Serum levels of naloxone will be measured before, at intervals during, and after the treatment period in order to measure bioavailability. The second phase of this protocol will study the efficacy of the maximally tolerated dose of naloxone (as determined in phase one) in patients with acute cerebral ischemia.